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When mission planners are considering different launch vehicles, what they take into consideration is how much mass each launch vehicle can lift into space. The Boeing Delta II launch vehicle was selected for the Mars Exploration Rover mission because it has the right liftoff capability for the weight requirements and because it's extremely reliable.
The Delta II family of launch vehicles has been in service for over 10 years and has successfully launched 90 projects including the last five NASA missions to Mars: Mars Global Surveyor and Mars Pathfinder in 1996, Mars Climate Orbiter in 1998, Mars Polar Lander in 1999, and Mars Odyssey in 2001.
Launch vehicle details
Deltas are expendable launch vehicles (ELVs), which means they are only used once.
The Rover A mission will use a standard Delta II 7925 when it launches (between June 5 and June 19, 2003). The later Rover B launch (between June 25 and July 15, 2003) will need more energy to get to Mars, so it will launch on a Delta II 7925-H, where "H" stands for "Heavy." Learn about the launch vehicle differences and the reasons for them.
The major elements of the Delta rockets for the MER missions, however, are nearly identical. Each launch vehicle consists of:
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Stage I:
Fuel and oxygen tanks that feed an engine for the ascent
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Solid rocket motors: Used to increase engine thrust; nine total, six of which are lit at liftoff, three a minute into flight
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Payload fairing:
Thin metal shroud or nose cone to protect the spacecraft during the ascent through Earth's atmosphere
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Stage II: Fuel and oxidizer and the vehicle's brains; fires twice, once to insert the vehicle-spacecraft stack into low Earth orbit and then again to orient the third stage prior to it firing
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Stage III: Solid rocket motor provides the majority of the velocity change needed to leave Earth orbit and inject the spacecraft on a trajectory to Mars; connected to the spacecraft until done firing, then separates
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